Instruction List (IL)

Instruction List

IL is an accumulator-oriented language: every instruction reads or writes a single implicit “current result” register and one operand. Closer to a PLC’s micro-instructions than to a general-purpose programming language.

Status in IEC 61131-3 third edition (2013): deprecated.

The standard committee marked IL as obsolete because its implicit single-accumulator model does not extend to modern PLCs (which all run multi-task ST/FBD code on top). matiec still accepts IL — round-trip parity for legacy PLCs and for the small number of IL POUs in older ForgeIEC projects. New POUs in ForgeIEC default to ST.

Sub-pages

• Mnemonics — full IL instruction-set reference: load/store, arithmetic, bitwise, comparison, branch, FB call, accumulator semantics, plus a step-by-step IL → ST migration table.